Conventional footwear typically includes an upper structure and a sole structure that cooperate to support a foot during use. The upper structure securely receives and positions the foot while the sole structure, which is typically secured to a lower portion of the upper structure and generally between the foot and a ground surface, attenuates reaction forces by absorbing energy as the footwear contacts the ground.
In addition to positioning a foot and absorbing energy during use, modern articles of footwear also concurrently provide a user with comfort, style, and enhanced athletic performance. For example, in one configuration, athletic footwear may provide an athlete with support and comfort during use while concurrently enhancing the athlete's traction and agility. Such a balance between function (i.e., support and comfort) and performance is often achieved through the materials and construction of the sole structure.
The sole structure may include a bladder that contains a fluid such as a gas or gel that provides improved cushioning and shock attenuation to the sole structure. The weight of the wearer and other loading on the bladder causes the fluid to displace within the bladder. As such, the bladder can more easily resiliently deform and/or more easily conform to the wearer's foot than some sole structures made entirely out of foam and rubber.
Bladders are often disposed between layers of the sole structure and, as such, are often blocked from view. Therefore, the wearer may not be aware that the footwear includes a bladder. In some cases, the sole structure includes an opening visually exposing the bladder. However, the opening is typically small, such that only a small portion of the bladder can be viewed, leaving the wearer unable to determine if the bladder is confined to the areas immediately adjacent to the opening or if the bladder extends into other portions of the sole structure. Furthermore, such openings often render the bladder vulnerable to damage from foreign objects.